WO2009141199A1 - Method for identifying an error function and in particular a drift of a rail pressure sensor in a common rail injection system - Google Patents

Abstract

According to the invention, in order to locate errors of the rail pressure sensor (38) when starting problems occur, the following method steps are proposed: determination of whether starting problems occur in the engine and if this is the case, an engine state is induced, in which the engine controller is already active but the starting phase of the engine has not yet commenced; substitution of the measured rail pressure sensor value used by the engine controller with a substitute value; start attempt of the engine and determination whether the engine has achieved an independent operation; and identification of an error function of the rail pressure sensor if the starting problems only occur when the measured rail pressure sensor value is used.

Description

description

Method for detecting a malfunction and in particular a drift of a rail pressure sensor in a common rail injection system

The invention relates to a method for detecting a malfunction and in particular a drift of a rail pressure sensor in a common rail injection system of a combustion engine.

Such a method is known for example from DE 10 2007 015 876 Al.

Modern internal combustion engines are provided with a common rail injection system, with which fuel is supplied by means of a pump in a pressure accumulator (common rail) and pressurized. The fuel is then injected from the common rail via controllable injectors into the combustion chambers of the internal combustion engine.

A common rail injection system is known for example from DE 198 34 660. The common rail is provided with a rail pressure sensor, with which the pressure in the rail is measured, wherein a function of the measured pressure

Pressure valve and / or the pump of the injection system is controlled and / or regulated. The (analog) pressure signal of the rail pressure sensor, which is processed in the control unit, so is the control variable for regulating the rail pressure. A malfunction of the rail pressure sensor or a drift behavior during operation and over the service life of the rail pressure sensor have a negative effect on the accuracy of the setpoint pressure to be set and thus on the accuracy of the injection quantity.

In the common rail injection system occurring component errors often lead to undesirable vehicle behavior such as poor or no longer possible engine start. On-board diagnostic Systems allow for starting problems only to a limited extent, for example in the case of an electrical short circuit, to determine the exact cause of the fault in the injection system without actively intervening in the system. This is especially true for a defective, for example, an offset, but electrically fault-free rail pressure sensor. Typically, it can then only be detected whether the rail pressure regulator is running against a limit without always being able to fully distinguish between whether a valve or the rail pressure sensor is defective, for example.

Due to this lack of knowledge of the exact cause of the error, often unnecessary or too many components are exchanged. For example, the described undesired vehicle behavior may initially lead to the replacement of the high-pressure pump, although the starting problem is actually caused by a drifted rail pressure sensor.

In order to be able to specifically carry out the corresponding repair in the event of a fault in the operation of an internal combustion engine, DE 100 40 254 B4 proposes a method for diagnosing a component, in particular a rail pressure sensor, of an internal combustion engine, in which a component which is responsible for an error only burnout misfires - can be causally causally, thereby Ü is checked that the internal combustion engine is deliberately brought into a test operating state in which the component for the error that has occurred can not be indirectly causal, and then checked whether the same error occurs. In detail, the targeted shutdown of the rail pressure sensor contained in a controlled system is discussed, wherein the pressure control valve is controlled after the shutdown so that the pressure in the rail assumes a so-called default pressure. As an alternative to bringing about the test operating state by switching off the component, it is also mentioned in the cited patent specification that the component, for example a sensor, be replaced by a model valid in certain operating states. It is proposed suggest in particular to calculate the signal supplied by a sensor from the signals of other sensors and to base the test operation of the internal combustion engine on this calculated size.

The object of the present invention is to provide a method which, in the case of starting problems of the engine, makes possible a diagnosis of the rail pressure sensor, in particular with regard to the presence of drift effects.

This object is achieved with the measures specified in claim 1. Preferred embodiments of the invention are set forth in the following subclaims.

The achievement of the above object according to the invention therefore comprises the following steps: determining whether starting difficulties of the engine occur and, if such occur, bringing about a motor state in which the engine control is already active but the starting phase of the engine has not yet started, replacing the measured, a rail pressure sensor value used by the engine controller by a substitute value for detecting a malfunction of the rail pressure sensor, starting the engine and determining whether the engine is in self-operation, and detecting a malfunction of the rail pressure sensor when the starting trouble occurs only when the measured rail pressure sensor value is used ,

The invention is based on the recognition that an activation of a substitute value on the rail pressure sensor value permits conclusions about existing or non-existing relationships between the starting problems and the rail pressure sensor. As a result, the invention makes it possible to limit the cause of the error in the injection system in the case of startup problems. Particularly preferred is an embodiment of the invention in which the implementation of the substitute value in a way the engine control almost überlistenden happening, the measured rail pressure sensor value is changed so slowly and steadily to the replacement value that the engine control diagnoses no electrical malfunction of the rail pressure sensor.

According to an advantageous refinement of these embodiments, the substitute value can be predefined in a simple manner by determining a rail pressure sensor value that is valid as a model in certain operating states of the starting phase of the engine and predefining it as a substitute value. Alternatively, in certain operating states of the starting phase of the engine, in accordance with the control strategy implemented by the engine control, valid rail pressure setpoint value can be adopted or modified and predefined as substitute value.

The method according to the invention is particularly suitable for execution in well-defined operating conditions, which are present above all in the workshop but, for example, also for stationary vehicle operating conditions (for example vehicle, start attempt by the driver). The malfunction detection can be advantageously carried out during vehicle operation on-board. According to a development of these embodiments, upon detection of a malfunction of the rail pressure sensor, the engine can be started and operated by permanent replacement of the measured rail pressure sensor value by the substitute value in a limp home mode with predetermined emergency running reactions.

For carrying out the method, a computer program can advantageously be used on a computer, which can be stored outside the vehicle or inside the vehicle, for example in the engine control or the transmission control. 1 shows a block diagram of a known from the prior art internal combustion engine with common rail injection system.

FIG. 2 illustrates the detection according to the invention of a defective rail pressure sensor. In the upper part of the diagram shown, the time history of the engine state in the starting phase and in the lower part of the diagram, the time profile of the rail pressure sensor value is shown.

Figure 3 illustrates, in the same representation as Figure 2, the inventive detection of a non-defective rail pressure sensor.

Figure 1 shows a sketch of a schematic diagram of a

Internal combustion engine with common rail injection system, wherein the internal combustion engine carries the reference numeral 10 as a whole. The engine 10 essentially comprises a combustion chamber 12, to which air is supplied via an intake pipe 14. The combustion exhaust gases are discharged through an exhaust pipe 16 with catalyst 18. Fuel passes into the combustion chamber 12 via high-pressure injection valves 20, to which fuel is supplied via a designated fuel rail 22 fuel manifold. This in turn is connected to a fuel tank 24 and is pressurized by a high-pressure pump 26. A pressure control valve 28 is connected on the one hand to the rail 22 and on the other hand with a return line 30 to the fuel tank 24 out.

In FIG. 1, spark plugs 32, which are fed by an ignition or annealing system 34, and a crankshaft 40 are also shown on the combustion chamber 12.

The internal combustion engine 10 further comprises an engine control unit 36, which is connected on the output side to the annealing system 34, the high-pressure injection valves 20 and the pressure control valve 28. On the input side, the engine control unit 36 receives signals from a rail pressure sensor 38 which controls the fuel pressure recorded in the rail 22. The rail pressure sensor 38, the pressure control valve 28 and the engine control unit 36 form a closed control loop for controlling the pressure in the rail 22. In dependence on the pressure signal provided by the rail pressure sensor 38 as well as the output signals of further sensors, the engine control unit 36 feeds the injector 20 Control signals that control the fuel metering. The injector 20 then injects the fuel stored in the rail 22.

The starting condition for the method according to the invention is that the engine start is no longer or only very badly possible. In the upper part of FIGS. 2 and 3, IGK means an engine state in which only the ignition lock (if implemented) and engine control 36 are activated. CRK means a state in which the engine is in the starting phase. Finally, IS / PL means an engine condition, such as idle or load, in which stable operation of the engine is achieved. The sections of the illustrated engine state curves correspond in time to the sections of the course curves of the rail pressure sensor value shown in the lower parts of the respective figures.

In section 1 of the engine state curve of Figure 2 and then there is a (first) starting the engine, which does not lead to an autonomous operation of the engine, but only up to the engine state CRK. 2 shows the rail pressure sensor value "PFU" respectively used by the engine control unit 36. In section 2 there is noticeably a minimal increase in pressure which, however, is insufficient for starting the engine the rail pressure sensor value, wherein the replacement pressure is connected in a delayed or steady manner, compare the rising curve in section 5, to the - measured - rail pressure sensor value in section 2. In section 4, a renewed tempering test takes place, in this case up to a stable Engine state with the engine running, Section 6. In the illustrated in Figure 2 In this case, after switching to the substitute value, an engine start is possible again, from which a faulty rail pressure sensor is concluded.

Also in the case of Figure 3 takes place in the period 3 a

Switching to the substitute value. Accordingly, although the rail pressure sensor value used by the engine controller 36 again increases to the substitute value, see section 5, the real pressure in the rail 22 indicated in the lower part of FIG. 3, see section 7, remains minimal, which is the case illustrated in the upper part of FIG Corresponds to the fact that the restarting in section 4 - despite replacement value - did not lead to an engine start (but only up to the engine status CRK). In this case, therefore, even after switching to the replacement value, an engine start is still not possible, from which it is concluded that the rail pressure sensor is not defective, so that further troubleshooting is required.

The test intervention according to the invention takes place in such a way that the measured rail pressure sensor value is replaced by a value predetermined within the test routine. This may be, for example, a setpoint value that is valid by the engine controller according to the control strategy or a value which is valid in the model, for example calculated. The engine controller uses or processes this replacement value in the same way as a measured rail pressure sensor value. Thereafter, a restart attempt of the engine is undertaken compare the respective sections 4 in FIGS. 2 and 3.

The relationship between system reaction and diagnosis according to the invention thus results essentially as follows:

If, after replacement of the measured rail pressure sensor value by the substitute value, an independent operation of the engine, for example idling, is achieved, then a defective rail pressure sensor, in particular a sensor drift, is detected. If not, this is interpreted as an indication that the Rail pressure sensor is functional. In this case further troubleshooting is required.

In on-board execution of the test routine according to the invention, if necessary sensor failure but possibly again an engine start and thus a vehicle operation possible. For this purpose, appropriate runflat reactions should be defined (e.g., MIL on, speed limit, etc.) to get the driver to visit a workshop.

Storing a corresponding error code gives the workshop the information to replace the defective rail pressure sensor, or allows in the error-free case (no sensor drift) a more targeted further troubleshooting.

Claims

claims 1. A method for detecting a malfunction and in particular a drift of a rail pressure sensor (38) in a common rail injection system of an internal combustion engine (10), comprising the following steps: Determining whether starting difficulties of the engine (10) occur and, if such occur, - causing an engine state (IGK) in which the engine control (36) is already active, but the starting phase (CRK) of the engine (10) has not yet started, Replacing the measured rail pressure sensor value used by the engine control unit (36) with a replacement value predetermined for detecting a malfunction of the rail pressure sensor (38), - Start attempt of the engine (10) and then determining whether an independent operation of the engine (10) is reached, - detecting a malfunction of the rail pressure sensor (38) when the starting difficulties occur only when using the measured rail pressure sensor value. 2. The method according to claim 1, characterized in that the measured rail pressure sensor value is changed so slowly and steadily to the substitute value that the engine controller (36) does not diagnose any electrical malfunction of the rail pressure sensor (38). 3. The method according to claim 1 or 2, characterized in that in certain operating states of the starting phase of the Engine (10) valid model rail pressure sensor value is determined and specified as a substitute value. 4. The method according to claim 1 or 2, characterized in that in certain operating states of the starting phase of Motors (10) in accordance with the control strategy implemented by the control strategy (36) valid rail pressure setpoint adopted or modified and specified as a substitute value. 5. The method according to any one of claims 1 to 4, characterized in that the malfunction detection is performed during vehicle operation on-board. 6. The method according to claim 5, characterized in that upon detection of a malfunction of the rail pressure sensor (38) of the engine (10) is started and operated by permanent replacement of the measured rail pressure sensor value by the substitute value in a limp home mode with predetermined emergency running reactions. 7. The method according to any one of the preceding claims, characterized in that a computer program for performing the method is used on a computer. 8. The method according to claim 7, characterized in that the computer program is stored in a flash memory memory of a vehicle-external automotive service device. 9. The method according to claim 7, characterized in that the computer program is stored in a flash memory memory of the motor controller (36).